Echos (Greek: ἦχος, ˈixos; pl. Echoi ἦχοι ˈiçi) is the name in Byzantine music theory for a mode within the eight mode system (oktoechos), each of them ruling several melody types, and it is used in the melodic and rhythmic composition of Byzantine chant ("thesis of the melos"), differentiated according to the chant genre and according to the performance style ("method of the thesis"). It is akin to a Western medieval tonus, an Andalusian tab', an Arab naġam (since 1400 "maqam"), or a Persian parde (since 18th century dastgâh).
Overview and semantics:
The noun echos in Greek means "sound" in general. It acquired the specialized meaning of mode early on in the development of Byzantine music theory since the Octoechos reform in 692.
In general, the concept of echos denotes the scale, intervallic structure as well as a set of more or less explicitly formulated melodic rules and formulae that represent a certain category of melodies within the musical genre. As such, echos is the basis for composing or improvising new melodies that belong to it, as well as for properly performing existing pieces that have been written in it. These rules include the distinction of a hierarchy of degrees (tones, notes), where certain degrees figure as cadence notes (ἑστώτες) around which the melody will revolve prominently, or on which the melody will end most of the time. However, only very late stages of the theory (19th-20th century) actually provide systematic descriptions of echoi, while earlier stages use mostly diagrams, indirect descriptions and examples. Explicit detailed descriptions must still be provided based on extensive analysis, as is the case with modal phenomena in numerous other cultures.
History and reconstruction:
Early treatises only state the initial or "base" degree which is the tone from which one starts chanting the scale of the echos, as well as its relative position within the overall scale of the echoi. More information on the structure of echoi is only indicated in a very rudimentary way through diagrams written in Byzantine music notation involving neumes. The details of the actual intervallic and melodic structure of echoi are virtually impossible to deduce from theoretical treatises prior to the 18th century. In fact, only relatively late systematic comparisons of the echoi with the makamlar of Ottoman court music, such as those by the Kyrillos Marmarinos, Archbishop of Tinos, in his manuscript dated 1747, and the western-oriented reform of the Byzantine notation by Chrysanthos of Madytos at the first half of the 19th century make it possible to understand the structure of echoi and to attempt reconstructions of melodies from earlier manuscripts.
Echos vs. maqam in eponymous compositional practice:
While in other traditions such as that of Ottoman music, the creation of new modes by eponymous masters resulted in a proliferation of modes (makamlar, maqamat), echoi are not attributed to specific composers, but are rather regarded as belonging to the collective and anonymous heritage of liturgical chant. Eponymous compositions do exist throughout most of the history of Byzantine chant, but their echos is always classified from within the system of existing echoi.
The system of echoi is rich and diverse. Closer study and comparison with modal systems of neighboring cultures reveals a complex network of cultural and ethnic influences throughout the century-old histories of the participating peoples. The basic theory of echoi is formalized in a system of eight modes called the Octoechos. See the article, Octoechos, for a discussion of its origins and a critique of this concept vis-a-vis actual practice.